Microfabrication technology is used to manufacture microfluidic devices such as lab-on-a-chip systems (“LOC”), which separate or mix fluids and perform biochemical reactions using the separated or mixed fluids. Microfluidic devices are also used to sort cells and provide a means to conduct single cell assays. Microfluidic devices include a substrate on which channels and chambers are formed. Soft lithography methods employing polymer-molding to generate LOC devices has enabled considerable innovation in the application of microfluidic devices for cell sorting and microcell culture. Precise control over laminar flow streams has enabled the selective spatial exposure of bioactive agents to cells and the investigation of mechanotransduction and cell response to shear stress under laminar or pulsatile flows. Precise control over solutions applied to the device enable control over the device function and application. Many challenges exist however, to creating a technology platform that can sort cells from a diverse population, maintain them in culture, uniformly direct their fate (e.g., differentiation, elimination) and interrogate cell signaling responses in situ as a function of cell density.
Parallel-plate microchannel systems employing physical features (pillars) and adhesive interactions have proven useful in cell separation. The pillars are generally fabricated by a reverse molding technique. FIG. 1 is directed to a prior art method 10 used to fabricate pillar arrays. A silicon wafer mold 12 is provided. Deep reactive ion etching (DRIE) is used to make pits 14 in silicon wafer mold 12. A hydrophobic material is coated onto silicon wafer mold 12 for easy removal of a polymer after it has been cured. A common polymer used in microfabrication of microfluidic devices is polydimethylsiloxane (PDMS). PDMS 16 is cast onto the hydrophobic silicon wafer mole 12 as shown in Step (a). In Step (b), the standard practice is to apply a vacuum to degas PDMS 16 and deplete trapped gas, for example, air, nitrogen, helium and/or argon, in pits 14 and dissolved in PDMS 16. PDMS 16 is then cured for example at 100° C. for two hours as shown in Step (c). The reverse molded pillar array 18 is removed from silicon wafer mold 12.
FIG. 2 shows a pillar array for use in cell separation. The disadvantage of pillar arrays is that, over time, as the adherent cell number builds, the microchannel hydrodynamic resistance and flow velocity can change. Devices can become clogged.
It is a primary object of the invention to provide a microfluidic device that can integrate cell sorting, microcell culture and real time diagnostics. It is another object of the invention to provide a microfluidic device that is applicable for use in diagnostic, therapeutic and investigative research, particularly in the areas of sorting rare cells and investigating stem cell and cancer cell biology. It is a further object of the invention to provide a facile and effective method of manufacturing microfluidic devices incorporating structures with novel geometries.